A MIM capacitor used in an analog device, a high frequency device or the like is miniaturized as the device is highly integrated. In order to compensate for reduced capacitance due to miniaturization, a dielectric film is required to be thinner. Thinning the dielectric film effects an increase in leak current. There is therefore a limit in thinning a dielectric film.
In order to prevent an increase in leak current and maintain a large capacitance, material having a higher dielectric constant than that of conventional SiON and the like is being adopted for a dielectric film. Examples of high dielectric constant material include alumina (Al2O3), tantalum oxide (Ta2O5) and the like. Titanium nitride (TiN) is generally used as the material of a lower electrode of a MIM capacitor.
If TiN constituting the lower electrode is exposed to oxidizing atmosphere during forming a dielectric film, the surface of the lower electrode is oxidized and a titanium oxide is formed. The titanium oxide formed on the surface of the lower electrode may cause an increase in leak current and a lowered manufacture yield. Oxidation of the TiN film can be prevented by forming an AlN film on the TiN film and forming an oxide dielectric film on the AlN film.
If a Ta2O5 film is formed on a lower electrode of Al and heat treatment is performed, an Al2O3 film can be formed at an interface between the Ta2O5 film and lower electrode of Al. A breakdown voltage can be increased by forming the Al2O3 film.